1. Field of the Invention
This invention relates to a timing module for use in a blasting system.
2. Related Art
Electronic detonators in a blasting system are typically interconnected through the use of elongate electrical conductors. The cost of the conductors, which are normally of copper, can be high and constitutes a significant part of the overall cost of the system.
Alternative approaches have been used to establish blasting systems. For example, detonators can be interconnected by using fibre optic cables. It is also possible to fire detonators, which are not physically interconnected, by using radio frequency signals. These techniques have, however, not been adopted on a large scale.
An electronic timing module is advantageous in that it can be programmed with a time delay which is executed in a highly reliable manner with a small error. Also, the time delay can extend over a lengthy period, several seconds in duration. Compared to this, a time delay which is generated using a pyrotechnical element is generally accurate only for a relatively short delay period. The accuracy is dependent on chemical and physical events and, inherently, it is usually not possible to generate a time delay period of several seconds duration with the same degree of accuracy as with an electronic timing module. On the other hand a pyrotechnic delay element is well-suited for use with a signal transmission device such as a shock tube which propagates a firing signal by means of a combustion, deflagration, detonation or similar event without using metallic conductors.
U.S. Pat. No. 5,133,257 describes an apparatus which includes a non-electrical ignition device and an electrical igniter which is responsive to the device. Use is made of a transducer for producing an electrical signal in response to a non-electrical energy input.
In U.S. Pat. No. 5,173,569, energy from a force produced by a non-electric, signal communication system (a shock tube), is converted to an electrical output signal and a time delay is then electrically generated. Similarly, WO 94/15169 describes a detonator assembly wherein energy from a non-electric impulse signal activates an electric delay circuit.
Chilean patent application No. 499-2010 describes a high precision delay system for the firing of a detonator wherein activation of a shock tube is detected by means of sensors such as electromechanical (impact), photoelectric, electroacoustic and piezoelectric sensors. In response thereto a detonator is fired.
The aforementioned techniques can substantially eliminate or reduce the use of interconnecting metallic conductors. However, some implementations are relatively expensive. Also, due care must be taken to prevent a detonator firing element from reacting to a detected characteristic which does not originate from a relevant shock tube.
For example, in the Chilean specification reference is made to repetitive sensing to verify “complete activation of the shock tube”. This is effected by detecting a light signal at two spaced locations on the shock tube. It is however not understood whether a procedure for verifying the source of the light signal is implemented, in order to avoid inadvertent firing of the detonator due to detection of an extraneous light source. In this respect it is pointed out, firstly, that light from an external source, which could be a light impulse or light from a constant light source, (not emanating from the shock tube in question) could be detected during one time window or during multiple time windows and such detection or detections could be treated as having come from the shock tube. Also, as a shock tube often includes an elongate tubular structure made from a light-transmissive plastics material, it is possible that light from a first shock tube could be emitted in a radial direction from the first tube, and impinge on a second, adjacent tube. Detection of light in the second tube could thus be linked, erroneously, to a shock tube event in the second shock tube and this could result in incorrect operation of a detonator system.
An object of the present invention is to provide a timing module which is responsive to predetermined input criteria, subject to validation thereof, in a reliable manner and which, at least in one embodiment when incorporated into a blasting system, allows for the substantial elimination of electrical conductors. The invention is described hereinafter with particular reference to a time delay which is directly associated with a detonator. This however is illustrative only. Various inventive principles described herein can be used in different ways. The timing module could for example be used at any location in a blasting system at which a time delay is required. The module can be used to generate a time delay on a surface between adjacent detonators which are connected to a harness in a blasting system.